<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style type="text/css">
		#outer {
            width:100%;
            margin:10px auto;
            text-align:center;
            font:12px/1.5;}
		#sum {
            margin:10px;
            display:inline;
            color:green;
        }
		#first,#second {
            margin:0 10px;
            width:50px;
        }
    </style>
</head>
<body>
    <div id="outer">
		<input type="text" id="first">+<input type="text" id="second">=<div id="sum">?</div><input type="button" value="求和">
	</div>
</body>
</html>
<script>
    /* 获取两个输入框的值和sum值 */
    var oInput = document.getElementsByTagName("input");
    for(var i=0;i<2;i++) {
        oInput[i].onkeyup = function() {
            this.value = this.value.replace(/[^\d|","]/,"");
        }
        oInput[2].onclick = function() {
            var f = document.getElementById("first").value;
            var s = document.getElementById("second").value;
            var oSum = document.getElementById("sum");
            var sum = 0
            console.log(oSum);
            sum += parseInt(f) + parseInt(s);
            oSum.innerHTML = sum;
        }
    }	
</script>